NOR can you call the edited assembly the complete source.
I disagree there. Let me make it clear that I'm taking about making major changes: so much so that the executable is substantially different from the original.
Not change a few text strings. Not fix a few trivial bugs. Changes that implement major new features, and touch a good deal of the generated assembly code[0]. Changes extensive enough that a reasonable person would no longer call the C code a "form" of the work, but a separate work.
I don't think an interpretation of the GPL that says "I wrote this code in C. Forever is C must it stay!" is correct.
If you could, the GPL would be pointless.
How so? Because someone making a change to my program could make it in a programming language I can't read? Yeah, I lose a lot of control over what people do with my software when I decide to make it Free. Tough.
[0] On a file-by-file basis, as that seems to be the most granular you can do with most compilers.